At gastrulation, mesoderm arises as a migratory germ layer that will participate to both foetal and placental development through region-dependant adaptation of cytoskeleton composition, cell shape and migration mode.

The cellular behaviours that underlie the internalization of the multilayered endoderm anlage in Xenopus laevis link the ancestral mode of vertebrate gastrulation to common, epithelial-based mechanisms of gastrulation in non-vertebrate animals.

In higher vertebrates, the position of the embryonic axis (the location at which gastrulation starts) is determined by the transcription factor Pitx2, which suggests that the mechanisms of this process, and hence those that regulate twinning, are related to those that set up the left–right axis.

Understanding the coordination of the forces generated in embryos by two processes, convergent extension and convergent thickening, is key to understanding how a hollow sphere of cells develops into an elongated embryo.

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